Mobile telephony networks have initially been conceived for allowing voice communications, in a way similar to the Public Switched Telephone Networks, shortly PSTNs, but between mobile users. The mobile telephony networks have experienced and are experiencing an enormous spread, especially after the introduction of second generation mobile networks, and particularly of digital mobile networks, such as those conforming to the GSM (“Global System for Mobile communications”) standard, and to the corresponding systems adopted in the United States and in Japan.
In way similar to the PSTNs, the second generation mobile networks are circuit switched networks; this greatly limits the bandwidth that can be allocated for a given user, especially in mobile networks of the second generation. On the contrary, data communications networks such as computer networks and, among these, the Internet, adopt packet switched schemes, that allow much higher data transfer rates.
Some solutions have been proposed for overcoming the limitations of the traditional circuit switched mobile networks such as the GSM networks, so as to allow the users of mobile terminals to exploit in efficient way the services offered through the Internet. One of the solutions that is acquiring a significant popularity is the GPRS (“General Packet Radio Service”). The GPRS is a digital mobile telephony technology compatible with the GSM networks (actually, it is built on the existing GSM network architecture) that allows data transfer at a higher speed than that allowed by the pure GSM. Essentially, the GPRS can be seen as an add-on to the GSM, that supports and enables packet data communication. Although third generation wireless communications systems such as those conforming to the standard UMTS (“Universal Mobile Telecommunication System”) are more promising in terms of data transfer speed, the GPRS may represent a prompt solution to improve the data exchange capability in existing GSM networks.
The services offered by these mobile networks in addition to the simple vocal communications have quickly increased in number and quality; just to cite some examples, in the last few years short messaging services (“Short Messaging System”, shortly SMS) and multimedia messaging services (“Multimedia Messaging System”, or MMS), and Internet connectivity services have been made available.
In particular, there is a strong interest in providing multimedia services to the users of mobile communications networks, i.e., services enabling the possibility of adding images, video, or access to data through the Internet or through the electronic mail, to a communication between users that is made of the sole voice. Among these services, the so-called “combinational services” are attracting great attention by the mobile telephony operators. For the purposes of the present description, by “combinational service” there is, in general, intended a service through which a terminal of a mobile communications network can simultaneously open and use two connections, typically a circuit (circuit-switched or CS) connection and a packet (packet-switched, PS) connection.
U. Olsson and M. Nilsson, in the article “Combinational services—The pragmatic first step toward all-IP”, Ericsson Review No. 2, 2003, describe, inter alia, an example of so-called “combinational services”, in which the ability to simultaneously handle traffic on a circuit connection and on a packet connection is used: the sharing of images during a conversation. The authors notice that the possibility of simultaneously handle traffic on a circuit connection and on a packet connection is allowed both with the WCDMA (Wideband Code Division Multiple Access), giving the possibility to use multiple and parallel bearers in the “over-the-air” interface (multiple Radio Access Bearers, multi-RAB), and with the GSM, in which a standardized mechanism—the Dual Transfer Mode, or DTM—yields similar possibilities. In the article, the authors notice however that the mere technical possibility of “successfully crossing the air” is not enough. Sometimes it is forgotten that the average final user is not interested in the complications of the channels coding and wave propagation. Instead, the final user wants a mobile terminal that is reliable, simple to use, and well adapted to the current context. In other words, some entity in the mobile terminal has to interpret what the user is trying to do and translate it into a sequence of operations.